Thermoelectric (Peltier) heat pump devices are essentially an array of thermocouples arranged in parallel to pump heat from one region to another. When used to cool a mirror surface, for example, heat is pumped from the reflective surface of the mirror to the surface on the opposite side. Although the array of elements are arranged in a series configuration electrically, the electrical resistance across the input terminals of the heat pump is very low, usually a fraction of an ohm. A typical heat pump input power requirement, for example, is 1.0 volt at 2.5 amperes. The heat pumping rate and, therefore, the temperature depression is controlled by the magnitude of the electrical power input. Heat pumps are normally driven by conventional linear power amplifiers which must be designed, with suitable dynamic range, for such purposes. Such linear power amplifiers, however, usually dissipate more power internally than is provided to the heat pump for pumping heat so that the overall system is extremely inefficient. In addition, the current drain on the input power source is very often intolerable in many applications. The input power requirement which has in the past been necessary for using a heat pump in cooling a mirror surface to its condensation point to measure humidity, for example, has in fact made the use of such linear power amplifier/heat pump combinations impractical for such a purpose, particularly in situations where large numbers of such humidity sensors are required, as in large industrial energy management systems.
It is desirable to provide a method and system of temperature control for humidity sensors in which power that is available on an input power line is converted efficiently on a demand basis for driving the thermoelectric heat pump therein in accordance with an input control signal. Such a system should provide suitable power conversion in which the internal power dissipation and, therefore, the input power requirement is reduced to a realizable minimum. The use of such a controlled power conversion technique should permit the use of a heat pump in humidity measuring instruments in which the overall level of performance represents a substantial improvement, at a reasonable and reduced cost, over that used by prior art humidity measuring systems.